BUG: listpri picked up non-priority patterns.

The regexp for the priority wasn't anchored to the beginning of the task. (As the filtering is done inside the _list pipeline, the task number has already been prepended.)
Also, by passing the regexp directly to _list, a case-insensitive search was performed, so despite [A-Z], lowercase characters were picked up, too. Need to make use of post_filter_command to inject a separate, case-sensitive grep into the pipeline.

Bonus: Added test for highlighting of listpri command.

todo.sh

@@ -1022,9 +1022,9 @@ note: PRIORITY must a single letter from A to Z."
         ## No priority specified; show all priority tasks
         pri="[A-Z]"
     fi
-    pri="($pri)"
 
-    _list "$TODO_FILE" "$pri"
+    post_filter_command="grep '^ *[0-9]\+ (${pri}) '"
+    _list "$TODO_FILE"
     ;;
 
 "move" | "mv" )